Optics Book Back Questions 10th Science Lesson 2
10th Science Lesson 2
2] Optics
Book Back Questions with Answer and Do You Know Box Content
Do You Know?
- Colloid is a microscopically small substance that is equally dispersed throughout another material. Example: Milk, Ice cream, muddy water, smoke.
- The lens formula and lens maker’s formula are applicable to only thin lenses. In the case of thick lenses, these formulae with little modifications are used.
Choose the best answers:
1. The refractive index of four substances A, B, C and D are 1.31, 1.43, 1.33, 2.4 respectively, the speed of light is maximum in
(a) A
(b) B
(c) C
(d) D
2. Where should an object be placed so that a real and inverted image of same size is obtained by a convex lens
(a) f
(b) 2f
(c) infinity
(d) between f and 2f
3. A small bulb is placed at the principle focus of a convex lens. When the bulb is switched on, the lens will produce
(a) A convergent beam of light
(b) A divergent beam of light
(c) A parallel beam of light
(d) A coloured beam of light
4. Magnification of a convex lens is
(a) Positive
(b) Negative
(c) either positive or negative
(d) Zero
5. A convex lens forms a real, diminished point sized image at focus. Then the position of the object is at
(a) Focus
(b) Infinity
(c) At 2f
(d) Between f and 2f
6. Power of a lens is -4D, then its focal length is
(a) 4m
(b) -40m
(c) -0.25 m
(d) -2.5 m
7. In a myopic eye, the image of the object is formed
(a) Behind the retina
(b) On the retina
(c) In front of the retina
(d) On the blind spot
8. The eye defect ‘presbyopia’ can be corrected by
(a) Convex lens
(b) Concave lens
(c) Convex mirror
(d) Bifocal lenses
9. Which of the following lens would you prefer to use while reading small letters found in a dictionary?
(a) A convex lens of focal length 5 cm
(b) A concave lens of focal length 5 cm
(c) A convex lens of focal length 10 cm
(d) A concave lens of focal length 10 cm
10. If VB, VG, VR be the velocity of blue, green and red light respectively in a glass prism, then which of the following statement gives the correct relation?
(a) VB = VG = VR
(b) VB> VG> VR
(c) VB< VG< VR
(d) VB< VG> VR
Fill in the blanks:
1. The path of the light is called as _______________.
a. beam of light
b. source of light
c. ray of light
d. angle of light
2. The refractive index of a transparent medium is always greater than _______________.
a. 1
b. 0
c. 1.5
d. -1
3. If the energy of incident beam and the scattered beam are same, then the scattering of light is called as __________________ scattering.
a. elastic scattering
b. Rayleigh’s Scattering
c. Mie Scattering
d. None of the above
4. According to Rayleigh’s scattering law, the amount of scattering of light is inversely proportional to the fourth power of its ______________.
a. focal length
b. refractive index
c. Wave length
d. Medium
5. Amount of light entering into the eye is controlled by _______________.
a. cornea
b. iris
c. pupil
d. retina
State true or false:
1. Velocity of light is greater in denser medium than in rarer medium.
2. The power of lens depends on the focal length of the lens.
3. Increase in the converging power of eye lens cause ‘hypermetropia’.
4. The convex lens always gives small virtual image.
Match the following:
Column – I Column – II
1. Retina – path way of light
2. Pupil – far point comes closer
3. Ciliary muscles – near point moves away
4. Myopia – screen of the eye
5. Hypermetropia – power of accommodation
Consider the statements given below and choose the correct option:
Mark the correct choice as
(a) If both assertion and reason are true and reason is the correct explanation of assertion
(b) If both assertion and reason are true but reason is not the correct explanation of assertion
(c) If assertion is true but reason is false
(d) If assertion is false but reason is true
1. Assertion: If the refractive index of the medium is high (denser medium) the velocity of the light in that medium will be small.
Reason: Refractive index of the medium is inversely proportional to the velocity of the light.
2. Assertion: Myopia is due to the increase in the converging power of eye lens.
Reason: Myopia can be corrected with the help of concave lens.
Answers:
Choose the best answer:
1.31 2. 2f 3. A parallel beam of light 3. Positive 4. Positive 5. Infinity 6.-0.25m 7. In front of the retina 8. Bi focal lenses
9. A convex lens of focal length 10cm 10. VB<VG<VR
Fill in the blanks:
1.Ray of light 2. One (1) 3. Elastic scattering 4. Wavelength 5. Iris
True or False:
1.False (Velocity of light is greater in the rarer medium than in the denser medium)
2.True
3.True
4.False (The convex lens forms enlarged and virtual image when placed between p and f)
Match the following:
1. Screen of the eye 2. Path way of light 3. Power of accomadtion 4. Far point comes closer
5. Near point moves away
Assertion and Reason:
- Both assertion and reason are true and reason is the correct explanation of assertion
- Both assertion and reason are true but reason is not the correct explanation of assertion